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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="spirit.notes.style_guide"></a><a class="link" href="style_guide.html" title="Style Guide">Style Guide</a>
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<p>
        At some point, especially when there are lots of semantic actions attached
        to various points, the grammar tends to be quite difficult to follow. In
        order to keep an easy-to-read, consistent and aesthetically pleasing look
        to the Spirit code, the following coding style guide is advised.
      </p>
<p>
        This coding style is adapted and extended from the ANTLR/PCCTS style and
        <a href="http://www.boost.org/development/requirements.html" target="_top">Boost Library
        Requirements and Guidelines</a> and is the combined work of Joel de Guzman,
        Chris Uzdavinis, and Hartmut Kaiser.
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Rule names use std C++ (Boost) convention. The rule name may be very
            long.
          </li>
<li class="listitem">
            The '=' is neatly indented 4 spaces below. Like in Boost, use spaces
            instead of tabs.
          </li>
<li class="listitem">
            Breaking the operands into separate lines puts the semantic actions neatly
            to the right.
          </li>
<li class="listitem">
            Semicolon at the last line terminates the rule.
          </li>
<li class="listitem">
            The adjacent parts of a sequence should be indented accordingly to have
            all, what belongs to one level, at one indentation level.
          </li>
</ul></div>
<pre class="programlisting"><span class="identifier">program</span>
    <span class="special">=</span>   <span class="identifier">program_heading</span> <span class="special">[</span><span class="identifier">heading_action</span><span class="special">]</span>
        <span class="special">&gt;&gt;</span> <span class="identifier">block</span> <span class="special">[</span><span class="identifier">block_action</span><span class="special">]</span>
        <span class="special">&gt;&gt;</span> <span class="char">'.'</span>
    <span class="special">|</span>   <span class="identifier">another_sequence</span>
        <span class="special">&gt;&gt;</span> <span class="identifier">etc</span>
    <span class="special">;</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Prefer literals in the grammar instead of identifiers. e.g. <code class="computeroutput"><span class="string">"program"</span></code> instead of <code class="computeroutput"><span class="identifier">PROGRAM</span></code>, <code class="computeroutput"><span class="char">'&gt;='</span></code>
            instead of <code class="computeroutput"><span class="identifier">GTE</span></code> and <code class="computeroutput"><span class="char">'.'</span></code> instead of <code class="computeroutput"><span class="identifier">DOT</span></code>.
            This makes it much easier to read. If this isn't possible (for instance
            where the used tokens must be identified through integers) capitalized
            identifiers should be used instead.
          </li>
<li class="listitem">
            Breaking the operands may not be needed for short expressions. e.g.
            <code class="computeroutput"><span class="special">*(</span><span class="char">','</span>
            <span class="special">&gt;&gt;</span> <span class="identifier">file_identifier</span><span class="special">)</span></code> as long as the line does not exceed
            80 characters.
          </li>
<li class="listitem">
            If a sequence fits on one line, put spaces inside the parentheses to
            clearly separate them from the rules.
          </li>
</ul></div>
<pre class="programlisting"><span class="identifier">program_heading</span>
    <span class="special">=</span>   <span class="identifier">no_case</span><span class="special">[</span><span class="string">"program"</span><span class="special">]</span>
        <span class="special">&gt;&gt;</span> <span class="identifier">identifier</span>
        <span class="special">&gt;&gt;</span> <span class="char">'('</span>
        <span class="special">&gt;&gt;</span> <span class="identifier">file_identifier</span>
        <span class="special">&gt;&gt;</span> <span class="special">*(</span> <span class="char">','</span> <span class="special">&gt;&gt;</span> <span class="identifier">file_identifier</span> <span class="special">)</span>
        <span class="special">&gt;&gt;</span> <span class="char">')'</span>
        <span class="special">&gt;&gt;</span> <span class="char">';'</span>
    <span class="special">;</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
            Nesting directives: If a rule does not fit on one line (80 characters)
            it should be continued on the next line intended by one level. The brackets
            of directives, semantic expressions (using Phoenix or LL lambda expressions)
            or parsers should be placed as follows.
          </li></ul></div>
<pre class="programlisting"><span class="identifier">identifier</span>
    <span class="special">=</span>   <span class="identifier">no_case</span>
        <span class="special">[</span>
            <span class="identifier">lexeme</span>
            <span class="special">[</span>
                <span class="identifier">alpha</span> <span class="special">&gt;&gt;</span> <span class="special">*(</span><span class="identifier">alnum</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">id_action</span><span class="special">]</span>
            <span class="special">]</span>
        <span class="special">]</span>
   <span class="special">;</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
            Nesting unary operators (e.g.Kleene star): Unary rule operators (Kleene
            star, <code class="computeroutput"><span class="char">'!'</span></code>, <code class="computeroutput"><span class="char">'+'</span></code>
            etc.) should be moved out one space before the corresponding indentation
            level, if this rule has a body or a sequence after it, which does not
            fit on on line. This makes the formatting more consistent and moves the
            rule 'body' at the same indentation level as the rule itself, highlighting
            the unary operator.
          </li></ul></div>
<pre class="programlisting"><span class="identifier">block</span>
   <span class="special">=</span>  <span class="special">*(</span>   <span class="identifier">label_declaration_part</span>
       <span class="special">|</span>   <span class="identifier">constant_definition_part</span>
       <span class="special">|</span>   <span class="identifier">type_definition_part</span>
       <span class="special">|</span>   <span class="identifier">variable_declaration_part</span>
       <span class="special">|</span>   <span class="identifier">procedure_and_function_declaration_part</span>
       <span class="special">)</span>
       <span class="special">&gt;&gt;</span> <span class="identifier">statement_part</span>
   <span class="special">;</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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